Systems employing wavelength-division multiplexed (WDM) optical signals can partition data into multiple data channels and encode each data channel on a monochromatic optical carrier beam having a different frequency. The monochromatic optical beams can then be combined into a single beam, thereby forming a WDM signal that may be transmitted through a single optical system, e.g., on the same optical fiber. Transmitting data using multiple optical carrier frequencies thus multiplies the data transmission bandwidth of an optical system when compared to systems using the same data encoding techniques on a monochromatic beam.
A receiver of a WDM signal typically uses the difference in the carrier frequencies to isolate or separate the individual frequency components. The individual signals can then be decoded to extract the received data. In general, such decoding employs photodiodes or similar light detectors that produce electrical signals corresponding to the separated frequency components, and the electric signals can be manipulated or processed using conventional electronic circuitry.
Free space optical communications avoid the complexity and cost of optical fibers or waveguides that carry optical signals from a transmitter to a receiver. However, the free space distance between a transmitter and a receiver typically makes alignment more difficult. Systems that tolerate these misalignments are thus desirable or necessary for free space optical communications. An alignment tolerant system for WDM optical communications would also be desirable to avoid the need for optical fibers or waveguides while providing a high data bandwidth.